I've been around a while. My thoughts.
NASA: They do alot of stuff right, and alot of stuff wrong. IMO, of course. Here in the east, the events tend to be 10lbs of shizzle in a 5 lb bag. NASA-SE and NASA-Mid Atlantic (formerly known as NASA-Virginia) are very active. SE goes to Road Atlanta, CMP, Roebling, Rockingham and I believe they have a Barber date (I'll be signing up to instruct there). Virginia primarily does Slummit Pt. and VIR, but eah track has several configurations.
SCCA: Old school. They want to race and autocross, and they are very organized and successful at it. If you are SERIOUS about racing, this is where it's at. Name a successful American professional sportscar racer, and I GARUNTEE they got their start in SCCA. A few regions are starting to do PDXs. NCR (North Carolina Region) does several a year. But SCCA tends to be stuck in it's ways and slow to change. This can be bad, or perhaps good. But SCCA has made more changes in the last 2 years than they did in the last 10. They are getting the message.
*IF* I ever start racing I will very likely start with SCCA.